The electrolytic decarboxylation of sugar acids has been employed in the production of xylitol and erythritol, as in U.S. Pat. Nos. 7,598,374, 7,955,489, and U.S. Patent Publication US 2011/0180418. For example, U.S. Pat. No. 7,955,489, describes the electrolytic decarboxylation of aqueous D- or L-arabinonic acid at specific ranges of neutralization—the ratio of alkali metal cations to arabinonic acid—to yield erythrose. Therein, the neutralization of arabinonic acid is maintained in solution by converting alkali metal araboninic acid salts to a protonated form using cation exchange resin and electrodialysis. Moreover, they describe adding un-neutralized arabinonic acid to the reaction solution over the course of the reaction to replace the arabinonic acid consumed at the anode.
Electrolytic cells can be constructed in many different configurations. However, all previously disclosed examples of carbohydrate acid electrolytic decarboxylations are carried out in single-compartment cells to maintain particular levels of neutralization. Too little neutralization results in a significant reduction in conductivity and reaction efficiencies, and too much neutralization can lead to reaction inefficiencies and product instabilities. Moreover, the presence of inorganic anions is detrimental to electrode life, reaction efficiencies, and downstream product purification efficiencies. Consequently the addition of non-reagent acids to control the degree of reactant neutralization is undesirable.
As sugar acids are often produced as alkali metal salts, there remains a need for cost-effective methods to maintain sugar acid neutralization without further conversion of alkali metal salts of carbohydrate acids with cation exchange resin, electrodialysis, or by addition of un-neutralized carbohydrate acids.